This invention relates to grease guns and particularly to a pressure relief valve for high pressure grease guns. More particularly, this invention relates to a pressure relief valve for use with high pressure grease guns of the type having a coupling secured to the outlet end of the gun which prevents grease from being ejected from the gun except when the coupling is properly located over a grease fitting.
Grease guns of the type with which the invention of this application is utilized are conventionally used in automobile service stations to grease bearings of motor vehicles. The gun is in reality a manually operated control handle for controlling a valve which in turn controls the flow of grease through the handle. When the valve of the gun or control handle is manually opened, it connects the outlet end of the gun to a high pressure grease pump. The pump is usually operable to supply grease to the gun at a pressure of approximately 7,000 pounds per square inch depending upon the resistance encountered by the grease in the bearing to which the grease is supplied. The greater the resistance, the higher the pressure of the grease ejected from the gun.
In addition to lubricant flow control handles of the type just described, there are also so-called "booster" control handles or guns for lubricating motor vehicles. Booster control handles are used for supplying grease at still higher pressures to vehicle bearings. A conventional booster control is operable to boost the ratio of grease pressure from the inlet to the outlet by a two-to-one ratio, i.e., from 7,000 to 14,000 p.s.i. Generally, booster control handles or guns are used to grease bearings of trucks or motor vehicles which are heavily loaded.
Irrespective of the type of gun or control handle which is employed for greasing or lubricating motor vehicles, some form of coupling unit is required by the gun and the grease fitting of the vehicle to interconnect the gun to the fitting. One type of coupling is a "fail-safe" coupling described in U.S. Pat. No. 3,788,427, assigned to the assignee of this invention, wherein the coupling has a valve contained internally of it which prevents grease from being ejected from the gun except when the coupling is properly located over a grease fitting. The coupling disclosed in the aforementioned patent eliminates the possibility of a mechanic either deliberately or inadvertently injecting himself with grease discharged through the grease gun and connected coupling.
Very nearly all high pressure grease guns contain a pressure relief valve to enable the gun to be removed or disconnected from "frozen" or "no flow" grease fittings. The necessity for this relief valve stems from the fact that most grease gun couplings include a piston or collet for clamping onto a grease fitting. If the fitting is frozen so that there is no flow through it, the collet becomes clamped onto the fitting by the grease pressure generally on the order of 7,000 pounds per square inch or more acting on the collet. The coupling can then only be removed by relieving the grease pressure behind the piston, and this is generally accomplished by opening the pressure relief valve. In couplings of the fail-safe type, it is possible for an operator to activate the gun and inadvertently fill the extension tube and coupling with high pressure grease. Because grease cannot be ejected through the coupling unless it is secured over a grease fitting, high pressure grease behind the piston prevents any rearward movement of the piston and thereby precludes the coupling from subsequently being attached to a fitting. Alternatively, if the coupling is properly located over a fitting but the bearing being lubricated by the fitting is frozen so that there is no throughput of grease, the grease pressure behind the piston may prevent the collet from being removed from the fitting.
In any of the situations just described, the pressure of the grease in the extension tube must be relieved. To that end, a relief valve is located in the extension tube. If this relief valve is opened to too great an extent or if the gun is equipped with a fail-safe coupling unit and the gun is activated while the coupling valve is closed and the relief valve open, high pressure grease is ejected through the relief valve and a dangerous condition obtains.
It has therefore been an object of this invention to provide a relief valve for a grease gun which eliminates or minimizes the possibility of a mechanic deliberately or inadvertently permitting high pressure grease to be ejected through the relief valve. That is, it has been an objective of this invention to provide a relief valve for a grease gun which eliminates or minimizes the possibility of grease being discharged through the grease gun flow control handle when the relief valve is open. To this end, the improved grease gun or control handle relief valve of this invention includes a pin valve mounted in the wall of the handle extension which is internally seated therein and spring biased to a closed position by an external spring and which is opened by the manual control handle engaging the valve stem but which cannot be opened except by movement of the control handle in a direction opposite that required to open the flow control valve to actuate the grease gun. Consequently, the gun cannot be actuated when the relief valve is open and the gun is fail-safe and high pressure grease cannot be either deliberately or inadvertently ejected through the relief valve.